The long-term goal of this project is to define the role of bioactive sphingolipid metabolizing enzymes in inflammation and to target these enzymes for novel anti- inflammatory therapy. The PI's laboratory has an established track record of expertise in sphingolipid metabolism and function. Studies from the previous funding period have led us into a novel exciting direction on the role and regulation of bioactive sphingolipid metabolizing enzymes in inflammation with strong possibilities for therapeutic development. Ceramidase and Sphingosine Kinase (SK) are two very critical enzymes in sphingolipid metabolism as they are implicated in the regulation of bioactive sphingolipid levels. Ceramidases breakdown ceramide to generate sphingosine, which is then phosphorylated by SK to yield sphingosine-1-phosphate (S1P). S1P, a highly bioactive sphingolipid, is produced in many inflammatory cells and acts both extracellularly and intracellularly on recently defined targets. S1P mediates/modulates several important biologic activities including inflammatory responses. Recently we have begun to uncover a specific role for acid ceramidase (AC) in inflammation in cells and in mouse models of inflammation. In addition, we have chemically synthesized several AC inhibitors and begun testing them for biologic activity. Our laboratory also pioneered studies on the role of SK1 in inflammation and we have specifically demonstrated a key role for SK1/S1P in regulating the induction of the cyclooxygenase (COX-2)/prostaglandin pathway in vitro and in mouse models of colitis and arthritis. In addition we have synthesized specific SK1 inhibitors and tested them for biologic activity. Importantly, our studies are leading us to appreciate complexities in vivo whereby altering the AC/SK1/S1P pathway in immune cells versus epithelial cells may differentially regulate inflammatory responses in mice. Moreover, our data show that SK1 has cardiovascular-sparing effects when compared with COX inhibitors. These data, therefore, lead us to propose the hypothesis that the AC/SK1/S1P pathway is a fundamental pathway in inflammatory diseases and that targeting the pathway may result in novel disease-modifying therapy in inflammation. This hypothesis will be addressed by the following Specific Aims: 1. Establish and define the role of AC in mouse models of inflammation. 2. Establish and define the role of SK1 in mouse models of inflammation. 3. Develop pharmacologic inhibition of AC and SK1 as novel inflammatory therapeutic targets. These compelling studies will not only implicate the pathway of AC/SK1/S1P at the center of the inflammatory process but will also begin to reveal clear and highly relevant differences over the COX-2 pathway that could lead to ground breaking novel anti-inflammatory therapy.